The present invention relates to wireless communications, and in particular to a radio subsystem for providing Local Multipoint Distribution Service (LMDS).
The ever-increasing demand for high-speed access to data networks, such as the Internet, continues to drive the need for new technologies in the computer and electronics industry. As the present day wireline telephone network strains under the demands of both corporate and individual need for high speed connections, a new world of computer communications will eventually break down into two domains, fiber networks and wireless networks.
Fiber networks provide a potential capacity for communication which is a factor of a thousand or even a million times greater than currently used copper cabling, while also providing signaling that is far less susceptible to errors. Wireless networks implemented using broadband technologies, such as LMDS, offer high capacity local access to remote networks that is less capital-intensive and faster to deploy than wireline solutions.
Through recent Federal Communication Commission (FCC) spectrum auctions in the United States, and similar activities in other countries, wireless networks implemented using LMDS are now becoming a reality for the delivery of a wide range of communication services. A point-to-multipoint radio access system implemented with LMDS is capable of providing services ranging from voice to high-speed data (e.g., speeds from T-1 up to OC-3) and serving customers ranging from small to large businesses.
Depending on the country, LMDS uses high frequency microwave signals in the frequency spectrum of 24 GigaHertz (GHz) to 44 GHz and higher for sending and receiving data signals (voice, video, Internet, etc.) wirelessly between radio equipment deployed at a central hub location and distributed remote locations. The radio equipment at the remote location is referred to as the customer premise equipment (CPE) and is typically located at the homes and buildings of LMDS subscribers. The radio equipment at the central hub location is referred to as the hub or base station equipment and is typically located at a central hub tower. Each central hub tower can serve hundreds or thousands of LMDS subscribers within a particular region (i.e., sector or cell site), while a master head-end coordinates the hub signals and connects the LMDS network to other networks via an Internet gateway and/or through land line cabling.
In a typical LMDS configuration, the primary functional modules of base station equipment are separated into an indoor unit (IDU) and an outdoor unit (ODU). The IDU includes digital equipment for transmission and reception of LMDS-compatible intermediate frequency (IF) signals. The IDU also performs the conversion between computer data signals of baseband frequency and the corresponding IF data signals. The IF data signals are typically transmitted between the IDU and the ODU over a coaxial cable connection. The ODU includes outdoor-mounted microwave equipment for wireless transmission and reception of LMDS RF data signals. The ODU also performs the conversion between LMDS-compatible IF data signals and the corresponding LMDS RF data signals.
In more detail, data transmission over an LMDS network involves an IDU that modulates computer data signals of baseband frequency into LMDS-compatible intermediate frequency (IF) signals having a frequency in the range between 10 MegaHertz (MHz) and 2 GHz using an LMDS modem module. LMDS modems are not typically provisioned to modulate baseband computer data signals directly into RF data signals having frequencies in the LMDS frequency spectrum. Instead, a coaxial cable connection carries the IF data signals from the IDU to an ODU where an IF/RF millimeter wave radio circuit performs a radio frequency (RF) up-conversion on the IF signals. The RF up-conversion shifts the carrier frequency of the IF data signals resulting in RF data signals having a frequency in the LMDS RF frequency spectrum. The RF signals are then transmitted wirelessly from an antenna packaged with the ODU to the associated customer premise equipment (CPE).
Conversely, data reception involves the antenna of an ODU receiving RF data signals transmitted wirelessly from the associated CPEs. The IF/RF millimeter wave radio circuit of the ODU performs an RF down-conversion on the RF signals resulting in intermediate frequency (IF) data signals suitable for demodulation by an LMDS modem module of an IDU. The intermediate frequency (IF) signals are forwarded over a coaxial cable connection to the IDU that demodulates them into corresponding baseband frequency data signals suitable for transmission over a computer network. The computer data signals are then transmitted to the computer network via an internetwork device (e.g., switch or router) or to a stand-alone computer.
Base station equipment in an LMDS network is physically separated into functional modules called indoor units (IDUs) and outdoor units (ODUs). The physical separation allows IDUs to directly interface with a computer network making installation and troubleshooting easier for network technicians. Similarly, ODUs can be installed up on a rooftop, tower, or pole above surrounding obstacles minimizing any signal interference during wireless transmission of LMDS RF data signals along a desired line-of-sight (LOS) propagation path within a sector or cell.
However, the separation of the base station equipment into indoor units (IDUs) and outdoor units (ODUs) makes managing this radio subsystem more complex. Since IDUs are directly connected to a computer network or stand-alone computer, IDUs can be easily managed from a network management system (NMS) server as another network device or end node. In contrast, however, ODUs are not directly connected to the network or stand-alone computer. Therefore, an NMS server indirectly manages an ODU through a communication path between an IDU coupled to the ODU.
Current deployment techniques involve complex and expensive cabling configurations in order to provide network management access to ODUs. In particular, common cabling configurations require direct cable connections capable of carrying network management signals between one or more IDUs and each ODU.
NMS servers provide the ability of managing and configuring devices through software. In the context of an LMDS wireless network, NMS servers are capable of obtaining status and telemetry information as well as providing command and control operation of base station IDUs and ODUs. An NMS server may be located on a computer network or may be a stand-alone computer. There may also be more than one NMS server on a computer network. NMS servers communicate with all of the equipment through the transmission of network management signals that implement a variety of proprietary and public management protocols, commonly SNMP. One or more IDUs typically serve as the interface for transmitting the network management signals between the NMS server and the ODUs.
FIG. 1A is a block diagram illustrating a common cabling configuration for providing network management access to ODUs. IDUs are omitted in FIG. 1A for purposes of clarity. The base station equipment 100 includes four ODUs, one ODU receiver 30 and three ODU transmitters 35-1, 35-2, and 35-3 (collectively referred to as the ODU transmitters 35). Each ODU 30 and 35 is coupled to an IDU via a power/data connection 25-1, 25-2, 25-3, and 25-4 (collectively referred to as the power/data connections 25) supplying DC power and carrying IF data signals. The power/data connections 25 are typically coaxial cables.
In addition to the power/data connections 25, each ODU 30 and 35 is coupled to a separate network management connection 27-1, 27-2, 27-3, and 27-4 (collectively referred to as the network management connections 27) that extends from one or more IDUs. The network management connections 27 are typically multi-conductor shielded cables. An NMS server (not shown in FIG. 1A) communicates with a particular ODU by transmitting network management signals over a network management connection 27 that couples an IDU to the ODU being managed.
In addition to having separate cabling connections for network management purposes, this cabling configuration requires additional network management connectors and port termination circuitry (not shown in FIG. 1A) at both the IDU and ODU ends adding to the overall time and cost of installation at a customer site. Furthermore, the existence of an additional connector in each ODU 30 and 35 presents another opening to seal for weatherproofing as well as another path for electrical surges (e.g., lightning) to potentially damage the unit.
FIG. 1B is a block diagram illustrating another common cabling configuration for providing network management access to ODUs. Regarding the base station equipment 200, there is no separate network management connection as in FIG. 1A. Instead, network management signals to and from each ODU are modulated over a low frequency carrier and multiplexed with the DC power and IF data signals on the power/data connections 25-1, 25-2, 25-3, and 25-4 (collectively referred to as the power/data connections 25). In this cabling configuration, network management signals are still transmitted directly from an IDU to each ODU being managed. The difference from FIG. 1A is that the network management signals are modulated over the power/data connections 25 rather than utilizing a separate network management connection to each ODU.
Although this configuration eliminates extra cabling and connectors dedicated for network management and avoids additional susceptibility to leaks and lightning, every IDU/ODU interconnection must still provide intermediate frequency (IF) data, DC power and NMS interface elements. Furthermore, in some cases more than one IDU device will be connected to a single ODU or the converse may be true. Management of such configurations is particularly complex for high capacity sites or sites capable of scaling to high capacity, which have increasing numbers of ODU transmitters. Such configurations become overly complex to effectively manage each ODU.
Embodiments of the present invention address these issues encountered in the actual deployment of LMDS or similar base station equipment. Embodiments of the present invention include a system for providing network management access to radio frequency (RF) outdoor units of base station equipment in a point-to-multipoint wireless network. This embodiment includes an RF outdoor unit (ODU) receiver, one or more RF outdoor unit (ODU) transmitters, and a frequency reference interconnection carrying a master frequency reference signal from the receiver to the transmitters. A network management signal destined for an ODU transmitter is modulated onto a low frequency carrier, which is duplexed with the master frequency reference signal and transmitted over the frequency reference interconnection for transmission from the receiver to the transmitter. Implementing either a public or proprietary management protocol, the network management signal is used for management and configuration of RF ODU receivers and transmitters. The low frequency carrier typically has a frequency lower than the frequency of the reference signal. Various digital modulation techniques may be utilized to modulate the network management signal onto the low frequency carrier including on-off keying, frequency shift keying, and dual tone multi-frequency.
The system for providing network management access to ODUs also includes an indoor unit (IDU). According to one embodiment, a network management connection couples the IDU to the ODU receiver and carries the network management signal from the IDU to the ODU receiver. Alternatively, a network management signal is transmitted from the IDU to the ODU receiver through a power/data connection that also couples the IDU to the ODU receiver. In particular, the network management signal is modulated onto another low frequency carrier. The modulated low frequency carrier is then multiplexed with the power and IF data signals over the same power/data connection from the IDU to the ODU receiver. The wireless network may implement a number of broadband technologies including LMDS.